1. Field of the Invention
This invention relates to an optical storage system and more specifically to a storage system comprising a fluorescent disc with many information layers and a drive for reading information from such a disc.
2. State of the Art
Single-layer (as well as two-layer) two-dimensional optical storage systems are widely used in existing devices. Most of the previous technical solutions in such systems of optical data storage were based on registering the change of reflected laser radiation intensity in the local spots (pits) of the data carrying layer. These changes could arise from light interference on the relief optical discs like CD ROM, from reversible polarization effects in magneto-optical or photoanisotropic media, as well as from reversible or non-reversible changes of reflection index in phase change media, or from dyes clearing up in “dye-reflection layer” systems, etc.
Three-dimensional (i.e., multilayer) optical memory devices provide higher capacity of recorded or stored data than two-dimensional systems. However, they have certain restrictions and additional requirements for construction and different features for recording media, and ways of recording and reading data, especially in the depth of the registering media.
In the reflection regime, every data-carrying layer of a multilayer optical medium requires a partly reflective covering. The use of such coverings reduces the intensity of both the reading beam and the reflected, data carrying beam as a result of direct and reverse passage through the medium towards the necessary data-carrying layer and back to the receiver. In addition, both coherent beams are subject to difficult-to-estimate diffraction and interferential distortions on the spots (pits and grooves) of the data-carrying layers while being transmitted.